The present invention relates to a material of a plasma display panel (PDP) used as a display device, and more particularly to a material for forming a protective film and a forming method thereof.
A plasma display panel is a display device in which a large number of minute sealed discharge spaces are provided between two glass substrates.
In an AC PDP commonly used at present, display electrodes of a front plate are covered with a dielectric layer and a protective film is formed on the dielectric layer that covers the display electrodes. This dielectric layer is provided for accumulating electric charge generated by voltage application to the electrodes. Further, the protective film is provided for preventing the damage on the dielectric layer due to the ion collision in discharge gas and for reducing the firing voltage by secondary electron emission.
In recent years, further improvement in efficiency (reduction of driving voltage) and improvement in display characteristics such as higher contrast have been demanded in PDP. In such circumstances, as a method for improving the efficiency of PDP, the increase of the xenon (Xe) concentration in discharge gas to about 15% has been examined.
However, the increase of the xenon concentration causes the problem of the increase of firing voltage and sustain voltage. Therefore, instead of magnesium oxide (MgO) which is a traditional material of the protective film, the use of calcium oxide (CaO), strontium oxide (SrO) and barium oxide (BaO) which are also alkali earth metal oxides and have higher secondary electron emission and the use of solid solution of these have been examined.
Japanese Patent Application Laid-Open Publication No. 2007-095436 discloses the use of calcium oxide (CaO), strontium oxide (SrO) and barium oxide (BaO) mentioned above.
Also, Japanese Patent Application Laid-Open Publication No. 2007-119833 discloses that a deposited film mainly made of strontium oxide (SrO) and calcium oxide (CaO) is formed as a protective film.
Japanese Patent Application Laid-Open Publication No. 2007-157717 describes that a first protective film made of a material having a work function lower than that of magnesium oxide (MgO) is formed and a second protective film containing magnesium oxide (MgO) is formed on the first protective film.
Japanese Patent Application Laid-Open Publication No. 2009-004150 describes that solid solution containing oxide of at least one element selected from a group including manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and zinc (Zn) is disposed in a shape of a protective film.
Japanese Patent Application Laid-Open Publication No. 2008-098139 discloses that a protective film is formed by using magnesium oxide (MgO) as a main component and two doping materials through vacuum deposition.
International Patent Publication No. WO 2006/049121: U.S. Pat. No. 4,343,232 discloses a protective film made of strontium oxide (SrO) and calcium oxide (CaO).